Unwrap Separate Meshes
As long as all the vertices in your objects are completely connected to each other (no loose parts) the following technique will work:


Select all your objects, and press CtrlJ. This will join them into one  mesh.
Press U > Unwrap (or whatever unwrapping method you want use).
Press P > Separate by Loose Parts.




This works great for quick 'n' dirty unwrapping onto a tileable image, but it may make more sense to link them all (like Matt said). The simplest way to link them early in a project is to duplicate them with AltD instead of ShiftD. It will link the mesh and the UV map which will make things easier later on.